Same issue here. I go to the play store, install one game then play and get no sound. Even if I install several games none will have sound.
Only way to get sound is to turn my phone off.
It might be worth getting in touch with the Smartphone Tech team by phone or live chat, and arranging sessions with the Remote Management team for them to have a closer look this for you.
I think you accidentally turned off sound on Game launcher
Go to game Launcher and at the bottom you have two options, one about the performance ans the other about the sound of games. As shown in the picture above